* \note \a y1, \a y2 can be negative, and put in ascending or descending order as well.
* \note \a data and \a y2 are evaluated only once, \a y1 twice.
*/
* \note \a y1, \a y2 can be negative, and put in ascending or descending order as well.
* \note \a data and \a y2 are evaluated only once, \a y1 twice.
*/